Wave signaling system



D 1929 L. A. HAZELTINE ec' wAvB SIGNALING SYSTEM Original -Filed Feb. 27, 1925 mi 'UW w J,

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Ressued Dec. 17, 1929 UNITED STATES PATENT OFFICE LOUIS ALAN HAZELTINE, 0F OAKLAND, CALIFORNIA, ASSIGNOR TO HAZELTINE COR- PORATION, A CORPORATION OF DELAWARE WAVE SIGN ALIN G SYSTEM Original application tiled February 2f?, 1925, Serial No. 12,000, and in Canada Hay 4, 1925. Original No.' 1,848,808, dated November 8, 1927. Divided and application led January 4, 1927, Serial No. 158,839, Patent No. 1,650,353, dated November 22, 1927. Application for reissue led February 14, 192s, serial No. 339,965.

This application is a division of my application Serial No, 12.000, filed February 27, 1925, Patent No. 1,648,808, granted November 8, 1927.

This invention relates to wave signaling systems, particularly radio receiving systems, and has for its object the provision of a radio receiver which is highly sensitive and highly selective and at the same time is simple to control. This result is accomplished primarily by employing tuned radio-frequency amplification, preferably in more than one stage, with the complete elimination of couplings between the plate circuits and the grid circuits, except through the mutual conductance of the amplifying vacuum tubes, which when they include three electrodes are sometimes called triodes, and with an arrangement of the amplifier transformers so that their input conductances are related in a certain way to the conductances of the vacuum tubes. Other features of the invention have to do with particular arrangements of the apparatus in ways that are both convenient and efficacious, as will appear in the discussion which follows.

The elimination of coupling between the plate circuits and the grid circuits is accomplished by the cooperation of three steps; first, the arrangement of the amplifier transformers so that there is no magnetic coupling between any two of them; second, the avoidance in the wiring of any substantial impedance common to two or more tuned circuits.; and third, the neutralization of the natural capacity coupling inherent between the tuned circuits, including particularly that due to the capacity between the grid and the plate of the vacuum tube.

The elimination of undesirable coupling' between the plate and grid circuits results in the prevention of feed-back or regenerative A action: and consequently there is no tendency towards the production -of local oscillations.

Such regenerative action is most troublesome with sharply tuned circuits and at .high frequencies.

The proper input conductance of the amplifier transformers is obtained by employing a primary winding of fewer turns than has previously been the practice; The results are: (1) high selectivity; substantially complete neutralization of'capacity coupling over a Wide range of frequency with fixed neutralizing adjustments, eventhough there be slight unavoidable deviations from the ideal conditions for neutralization; and (3) higher amplification than is obtained with the large number' of primary turns previously customary.

Referring to the drawings: I

- Figures 1a and 1h show a plan and an elevation, respectively, of a tuned radio-frequency amplifier embodying the features of this invention.

Figure 1 shows the diagram of connections o f the receiver of Figures l and 1".

Figure 1c1 shows the structure of the radiofrequency amplifier transformers of Figures 1a and 1b.

Figure 1e shows a modification of the circuit of Figure 1.

In the radio receiver represented inI Figures 1a and 1b there are three radio-frequency transformersvfll., T1, T2, each associated with a tuning condenser Ca, C1, C2. Each coil is mounted on the'back of its condenser for the purpose of keeping as short as possible the leads between them, and for other purposes as disclosed in my U. S. Letters Patent Nos.

1,577,421 and 1,698,364. The vacuum tubes are mounted adjacent to the coils and condensers with which they are associated, also t in order to keep the connectingr leads as short two of the transformers, as described in my two patents above referred to. Care is also taken to avoid magnetic coupling between stages that might be due to closed conducting loops linked with the fields of two or more transformers. Such loops might exist in a supporting metal framework, or in the leads from the batteries, which leads are therefore preferably hunched together.

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Figure 1 shows the diagram of connections` for the receiver of Figures 1* and 1". The reflex principle is emp o ed by `which `radio-frequencyamplifying tu es A1 and A2 quency current, by-pass condensers C, A 1 CD1,

,2, Cm are arranged to provide low-1m oedance return paths for the radio-frequincy grid` and plate currents direct to the respective filaments, or cathodes. This keeps radiof frequency currents. but of the common battery leads, which may have sufficient reactive im edance as to cause objectionable coupling if t ey'carry radio-frequency currents of di ferent stages. The grid by-pass capacities C51, C maybe of the order of one ten-thousandth microfarad, and the plate by-pass capacities, CP1, 0,2, CN, may be of the order of one thousandth microfarad, these values givin low radio-frequency impedances but sufficiently high audio-frequency impedances not to shunt unduly the audio-frequency transformer coils and so lower the audio-frequency amplification. The leads to the bypass condensers should be shortl to minimize their reactive impedances.

In case the radio-frequency current in the plate circuit of detector tube D passes in appreciable amount through the primary of Ta1 and so couples tube D with tube A1, then a radio-frequency impedance Lpd (Fio'ure le) may be inserted in the lead from the plate ofv tube D, and a condenser Cpd may be connected directly from this plate to the filament. Care must be taken that the impedance coil Lpd is not coupled magnetically to any of the radio-frequency transformers.

The filament system should be grounded, preferably at X, Figure 1, so that radio-freuency current passing from the antenna t rough the natural capacity between the coils of Ta' will flow directly to ground and not through the battery leads to the other tuned circuits and thence through their natural capacities to ground, which would result in undesirable coupling between the stages.

oupling between the plate circuit and the 'grid circuit of tube A1, due to the natural capacity Cc,- between the grid with its connected apparatus and the plate with its connected apparatus, is neutralized by the neutralizing capacity Cm connected between the grid and the auxiliary coil ab, which in Figure 1C is a portion of the secondary coil ac of transformer T1. As explained in my U. S. Letters Patents No. 1,489,228 ard No. 1.533,858, neu- Figure 1d shows the .construction of thel transformers'l1 and T2. The primary winding de is mounted so as to have close magnetic coupling to the tapped portion ab of the seeondary coil ac, Athe tap. b connecting to the neutralizing condenser Cm, or Cu2, as shown in Figure 1c. To make the lcoupling asclose ,as possible between the auxiliary `coil ab and the radio-frequency plate circuit, the leads from d and aand the leads to the plate bypass condenser (1,1 or CD2, Figure 1, should be made as short as possible. Such closeness of coupling is needed because the radio-frequency current flowing conductivel through p the plate of the vacuum tube woul' build up an appreciable voltage in the leakage reactance of the plate circuit, which voltage would not be balanced by a voltage in the auxiliary coil ab. The primary and secondary coils in Figure 1d are wound in the same direction, with the result that terminal a connecting to the filament system, Figure l, is of opposite iolarity to terminal e also connected to the filament system, (or, in other words, the lowpotential terminals a and e are of opposite polarity, and the same is therefore true of the high potential terminals c and d) as required for the purpose of neutralization. The connection ofthe neutralizing condenser to a tap b so that ab is a small portion of the secondary winding allows close coupling to be obtained between ab and de and at the same time requires the primary winding de to extend un'- der only a small portion of the secondary, thus ininirnizinor natural capacity and dielectric loss due to the dielectric field between primary and secondary. The primary winding, as indicated, is placed adjacent to the` filament end'a of the secondary winding, for the same purpose.

In addition to the direct magneticv coupling between the primary coilde and the auxiliary or neutralizing coil ab, of Fig. 1d,

there exists also an indirect coupling between i those coils due, first, to the direct magnetic coupling betweenvthe primary coil de and the secondary coil ac, and, secondary, to tlie connection of a tuning condenser C1 at the terminals a and c of the series-connected coils ab and bc. This indirect coupling substantially improves the neutralization under operating conditions (especially at ,reso-k nance) by effectively' increasing the coupling Aance with the followin procedure.

between the primary coil de and the neutralizing coil ab.

In general there will exist natural capacity between the apparatus connected to the grid of A1 and apparatus connected to the grid of A2. Such natural capacity has a neutralizing tendency and so in part supplants Cm. This neutralizing capacityis relatively more effective,for a given value,as the ratio of turns of acto de is greater than that of ab to de. Since ac is not so closely coupled to de, such neutralization is not ideal and therefore should be minimized. rThis may be accom- "shed by making as short as possible all iaads connecting to the grid, and by employing tuning condensers of the shielded ty e or l a grounded metal yplate on the back o the anel. Other grounded conductors, such as .the battery leads and the audio-frequency transformers, interposed in the dielectric fields between the tuned circuits also serve as partial shields.

On accountY of the diiiiculty of accurately measuring or calculating very small capacities, particularly natural capacities, the proper neutralizing capacities Cm and C22, Figure 1, are in practice determined by trial. A suggested procedure for neutralizing is as follows: First, with they filament of A2 cold and those of A1 and D lighted, a strongsignal is tuned in, as heard on a telephone receiver plugged in the detector plate circuit; C22 is then adjusted until the signal disappears, showing that no coupling exists between the plate circuit and the grid circuit of A2. Then with the laments of D and A2 lighted and that of A1 cold, -the process is repeated with C21.

On' account of the proximity of the radiofrequency transformers to one another and more es ecially of the presence of a loop formed y the. leads between each secondary and its tuning condenser, the actual coil `inclinationv for zero magnetic coupling may differ slightly, but appreciably, from its theoretical value of substantially 5 5 degrees. Hence, Athe roper inclination must also be determined y trial, and may bein accord- With all coils at the same inclination, Cm and C22 are adjusted for zero coupling as described in the preceding paragraph, with the circuits tuned first for alow frequency and then for a high frequency. In general, the settings found for the two frequencies will be different, showing that the capacity cou ling, which varies with the frequency, is ing called upon to compensate for some magnetic cou ling. The coil inclinations are then varied together, until the settings of C and C2 are found to be the same at thetwo extreme frequencies. y

The determination of the proper coil angle need ordinarily be made only once for a given design of receiver, but the adjustments of the neutralizing capacities are made in each individual receiver.

The use of short grid leads, the separation of the tuned circuits, and the interpositionof grounded conductors, all serve to minimize the natural capacity coupling between T2 and T2, Figure lc. In addition, the antenna leadinshoul'd' be kept, as indicated, at the end of the receiver remote from the circuit of T2; and ungrounded conductors should not be allowed to extend from the neighborhood of Ta to the neighborhood of T2. By taking these precautions, the natural capacity coupling between T,L and T2 may be substantially eliminated, and so need not be neutralized. heny the telephone receiver is plugged into thethird jack J2, the plate and gridcrcuits of the tube A1 will have the same natural audio frequency if the transformers TE,1 and T22 are alike. This would tend to give considerable audio-frequency regeneration due to the coupling capacity C61 between the plate andthe grid of A1. This coupling capacity will be neutralized by Cm for audio requency, provided the ratio of turns in the audio-frequency transformer T22 is the same as the ratio of turns ofab to de and its relative polarity is as indicated,'-that is, the same condenser vserves to neutralize capacity coupling both at radio frequency and at audio frequency.

We will now consider the Aproper Value of the effective ratio r of secondary turns ac to primary turns de in the amplifying transformers. (By effective ratio is meant the ratio .that would give the same mutual inductance with the same secondary self-inductance ifl the coupling between primary and secondary had a coefiicient of unity. If the coupling is actually less than unity, the number of primar turns must be correspondingly increased re ative to the number of secondary turns. yThe amplification for one stage 1s given y the expression g1 T291 (2) which hasvits maximum value when Since at resonance the input conductance of the transformer 1s equal to lrag., the last condition may be expressed in the form: that the amplification at resonance is a maximum when the ratio of turns of the transformer is so chosen that the input conductance of the transformer is equal to the plate conductance of the vacuumtube. If the number of primary turns, is reduced below/this value, the amplification falls off, but less rapidly at resonance than at other frequencies. For example, if the number of primary turns is halved' relative to its value for maximum resonant amplication, the amplification at frequencies far from resonance is also halved, but the amplification at resonance is reduced only twenty per cent. The result is a decided gain in selectivity, since interfering signals are weakened proportionately more than the signal tuned in. Thus to obtain high selectivity together with good amplification, the ratio of turns should be so chosen that the input conductance T29s is substantially, but not greatly, higher than the plate conductance gp.

The following values are representative of present day practice in radio telephone broadcast reception:

=85 I w 5 radlans per microsecond; L,=0.25 millihenry;

0', @E 0.16 millimicrofarad gs=0005w0s=004 millimho (this value y includes the conductance of the coil Ls, that of the condenser C5, and that of the grid-filament circuit, t-he last ordinarily being negli gible When a grid bias is used, as by the bat tery Bc, Figure 5u) If We use one-half the optimum number of primary turns, the effective turn ratio will be Jill- T12 gh 2 0.004 l0.

The amplification at resonance is then Vith t-he form of transformer shown in Figure 1d, the following design data will give constants approximating those listed in the preceding paragraphs: secondary coil, 60

`turns of N o. 24 A. W. G'. double-cotton-covsiderable step-up ratio, the capacity and resistance of the antenna are equivalent to much smaller capacity and resistance in the secondary circuit.

Vith the antenna polarity indicated for Ta, Figure 1c, adjacent turns of primary and secondary are at the same radio-frequency potential; so there is no dielectric field between primary and secondary, as there is in T`1 and T2. 'Hence, Ta has less natural capacity thanvT,L and T2, which tends to compensate for the capacity added by the antenna. The three condensers being alike, the three tuning dials represented in Figure 1b will thus read nearly alike when all are adjusted to any one frequency. This greatly simplifiesI the process of tuning the receiver. The result just described, i. e., that all tuning` dials will read substantially alike when in proper adjustment for reception is, of course, 'dependent on the absenceof regenerative action and contrasts with prior receivers employing tuned radio-frequency amplification without thefelimination of undesirable coupling between stages, for in such receivers detuning of the amplifier output circuits was ordinarily necessary for the control of regeneration and oscillation, and, in any case, the tuning adjustment was dependent upon the regeneration present, and therefore upon the state of the batteries and of the vvacuum tubes.

I claim:

1. A sharply selective, radio-frequency amplifying receiver comprising a triode having a grid, a plate and a cathode; means for applyingadio frequency waves across said grid and' cathode; a radio frequency transformer of t-he air core type comprising a primary coil of a few Vturns and a spaced secondary coil of more turns coupled to said primaryv `coil so that substantially sharp, independent tuning of said secondary coil may be effected; a varlable condenser for tuning said secondary coll; an amplifymg source of direct current energy; circuit connections from said plate through said primary coil and said source to said cathode and from such terminal of said secondary coil to said cathode that a connection to said grid from said limitingV condenser. v

2. The receiver as defined in claim 1 and further characterized by the following that a second similar triode has connections across its grid and cathode from the te'rninals of said secondary coil whereb said second triode is responsive substantially only to the Wave energy transferred from said primary coil to said secondary coil; a second similar air-core radio frequency transformer with its'cprimary coil energized from the plate of sax current energy; terminals of unlike polarity of the primar-y and secondary coils of said second transformer being connected to the cathode of said second triode; a second variable condenser connected across the terminals of the secondary coil of said second transformer for selective tuning substantially independently; and a second reverse feed back coupling substantially to neutralize the' grid and plate feed backcoupling associated withsaid second triode comprising a limiting condenser of suitable low capacity, a tapoff from a suitable potential point on said secondary coil to said limitingl condenser and a connection to the grid of said second triode from said limiting condenser.

3. In an amplifier, a vacuum tube provided with a grid, a filament, and a plate, a grid circuit, a plate circuit, inherent capacity coupling between said grid circuit and said plate circuit, an output transformer associated with said lat-e circuit and having primary and secon ary windings, a tap on said secondary winding, and a neutralizing capacit connected between said tap and said gri said primary winding being placed in proximity to the portion of said secondary winding included between the tap and the low-l potential end of said secondary winding, whereby natural capacity and dielectric loss due to the dielectric field between said primary and secondary windings are minimized.

4. In an amplifier, a vacuum tube provided with a grid, a filament and a plate, a grid circuit, a plate circuit, inherent capaclty cou.

plingbetween said grid circuit and said plate c1rcuit',an output transformer associated with ,said plate circuit, said output transformer comprising a single-layer secondary coil having a tap and a single-layer primary coil placed in close proximity to the turns of said secondary coil included between the tap and the low-potential end of said secondary coil, whereby the coupling between the primary coil and said turns of the secondary coil is close, and a neutralizing capacity connected between said tap and said grid.

5. In an amplifier, a vacuum tube provided with a filament, a grid, and a plate, a grid circuit, a 'plate circuit, capacity coupling between said plate circuit and said grid circuit,

an output transformer associated with said plate circuit, said output transformer comprising a single-layer Secondary 'coil provided with a tap and a single-layer primary coil placed in close proximity to the turns of said secondary vcoil included between the tap and the low-potential end of said secondary coil, a direct low-impedance path from the plate to one terminal of said prlmary coil,

second triode and said source of direct.

a direct low-impedance path from the other terminal of said primary coil to the filament, whereby the coupling between the plate circuit and said turns of the secondary coil is close, anda neutralizing capacity connected from said-tap toA said grid.

6. In anamplifier, a vacuum tube having a grid, a plate, a filament and glrid-plate capacity coupling through whic a' capacity current flows from late to grid, and ymeans for neutralizing saidlgrid-plate capacity` cou. pling, said means including a first coil connected in the plate-filament circuit of said amplifier, a tuning condenser, af second coil coupled to said first coil by means including said tuning condenser, and a neutralizing capacity couplin said grid with said second coil and there y conductin said capacity current away from said gri 7. In an amplifier, a vacuum tube having a grid, a plate, a filament and grid-plate capacity coupling through which a capacity current flows from late to grid, and mea-ns for neutralizing sai' grid-plate capacit coupling, said means including ,a first co connected inthe plate-filament circuit of. said amplifier, a tuning condenser, a second coil coupled to said first coil by means including magnetic 4 coupling and said tuning condenser, and a neutralizing capacity coupling said gridwith said second coil and thereby conducting said capacity current away from said rid.

8. n an. amplifier, a vacuum tube having a grid, a plate, a filament and grid-plate capacity coupling through which a capacity current flows from plate to grid, and means for neutralizing said grid-plate capacity coupling, said means comprising a first coil electricall coupled with the plate-filament circuit o said vacuum tube, a tuning condenser, a second coil coupled by said tuning condenser to said first coil, and a neutralizin capacity coupling said second coil with sai grid and thereby conducting said capacity current away from said grid.

9. In anamplifier, a vacuum tube having a grid, a plate, a fila-ment and grid-plate capacity coupling, and means for neutralizing said grid-plate capacity coupling, said means comprising a first coil connected in the plate-filament'circuit of said vacuum tube, a second coil coupled magneticall to i means comprising a primary inductance coil coupled by said tuning condenser to said second coil, and a neutralizing capacity coupling said third coil with said grid.

11. Inan amplifier, a vacuum tube having a grid, a plate, a. filament and grid-plate capacity coupling through which a ca acity current flows fromvplate to grid, a sing e coil connected in the plate-filament circuit of said vacuum tube, al pair of coils connected in series at a junction point, magnetic couplin between said single coil and at least one o said pair of coils, and means for neutralizing said grid-plate capacity coupling, comprising `a neutralizing capacity couplin grld with said junction point and t ereby conducting said capacity current away from said grid. n i

12. An amplifying vacuum tube provided with a grid, a filament, a plate, a grid circuit and a plate circuit; inherent capacity cou-l pling between said grid circuit and said plate circuit, through which capacity coupling a capacity current flows from plate to grid; an

output transformer comprising. a primary coil connected in said p tuned secondary coil having a tap intermediyate the ends thereof; and a neutralizing capacity connected between said grid and said tap and serving to conduct said capacity c urrent away from said grid; l

13. A multi-stage radio-frequency amplifier comprising in each sta e a vacuum tube having a grid,a plate, a ament, and ridplate capacity coupling, the vacuum tu e in a certain stage being coupledl to that in the next succeeding stage by a tuned coupling system, said coupling system comprising three coils in a unitary structure and a tuning coudenser connected-between the grid and the filament in said succeedin stage, the first of said coils being connecte ment circuit of said certain stage and havin reversed close magnetic coupling with one o the other two coils, said other'two coils being connected in series between the terminals bf saidl tuning condenser and having capacity coupling between their junction point and the grid of the vacuum tube in said certain stage, and means for preventing undesired magnetic coupling between stages.

14. In an amphfier, a vacuum tube having a grid, a plate, a filament and grid-plate capacity coupling thru which capacity current flows from plate to grid, and means for neutralizing said grid-plate coupling, said connected in the plate-filament circuit of said vacuum tube, a secondary inductance divided at a junction point into two coils one of which comprises a lar er value of inductance than the other, one oi said two coils being directl coipled magnetically to said primary coi sai two coils being electrically coupled by means including a tuning condenser connected across-'their extreme terminals, whereate clrcuit, and al whereby to conduct said capacity currentaway from said grid.

In testimony whereof I aiiix my signature.

LOUIS ALAN HAZELTINE.

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